Ammonia is a widely used chemical with many applications. Some of these applications are (but not limited to): a) reductant for selective catalytic reduction (SCR) of NOx in exhaust from combustion processes, b) ammonia used as an energy carrier for a fuel cell or c) ammonia used as a reactant or additive in a chemical reaction. For most applications, the storage of ammonia in the form of a pressurized liquid in a vessel is too hazardous and a storage method involving absorption in a solid may circumvent the safety hazard of anhydrous liquid ammonia.
Metal ammine salts are ammonia absorbing materials, which can be used as solid storage media for ammonia (see, e.g. WO 2006/012903 A2), which in turn, for example, may be used as the reductant in selective catalytic reduction to reduce NO emissions, see e.g. WO 1999/01205.
Usually, ammonia is released by thermal desorption, e.g. from metal ammine salts, by external heating of a storage container, see e.g. WO 1999/01205. The heating elements may also be placed inside the storage container, see e.g. U.S. Pat. No. 5,161,389 and WO 2006/012903 A2.
WO 1999/01205 discloses the use of ammonia as the reductant in selective catalytic reduction to reduce NOx emissions from automotive vehicles. The ammonia is released from an either adsorptive or absorptive solid storage medium, among others Sr(NH3)8Cl2 or Ca(NH3)8Cl2 in granular form, in a storage container and temporarily stored as a gas in a buffer volume. The amount of ammonia to be supplied to a reaction volume in the vehicle's exhaust system is dosed under the control of an electronic engine controller according to the current operating state of the engine (WO 1999/01205, p. 9, last para.). The amount of ammonia to be desorbed from the storage medium is, for example, controlled by a feed-back control in which the pressure in the storage container is measured by a pressure sensor, and if the pressure reaches a pressure threshold, the supply of heat is interrupted (WO 1999/01205, para. bridging p. 8 and 9).